Polymerization processes using aliphatic maleimides

ABSTRACT

Aliphatic maleimides and methods using the same are disclosed. Polymerization of compositions which include the compounds of the invention may be activated by irradiating the composition with radiation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. Ser. No. 08/917,024 filed Aug.22, 1997, U.S. Pat. No. 6,034,150 which is related to commonly ownedcopending Provisional Application Serial No. 60/024,546, filed Aug. 23,1996, and claims the benefit of its earlier filing date under 35 U.S.C.119(e).

FIELD OF THE INVENTION

This invention relates generally to maleimide compounds and methods ofusing the same as photoinitiators in photoactivatable polymerizationsystems.

BACKGROUND OF THE INVENTION

Ethylenically unsaturated compounds, such as acrylate derivatives, canbe polymerized by exposure to radiation, typically ultraviolet light, inthe presence of a photoinitiating system. Typically, the photoinitiatingsystem includes (1) a compound capable of initiating polymerization ofthe ethylenically unsaturated compound upon exposure to radiation (a“photoinitiator”) and optionally (2) a coinitiator or synergist, thatis, a molecule which serves as a hydrogen atom donor. The coinitiatorsor synergists are typically alcohols, tertiary amines, amides, or etherswhich have labile hydrogens attached to a carbon adjacent to aheteroatom.

Numerous photoinitiators with varying structures are commerciallyavailable for use in different systems. However, nearly all commerciallyavailable radiation curing processes require an initiator incorporatedinto the formulation, a large percent of which is not consumed. The useof conventional photoinitiators typically results in the production ofsmall molecule photo-byproducts. The presence of the residualphoto-active compounds and extractables can result degradation of thephysical properties of the article, such as decreased light fastness,discoloration, and lower resistance to oxidative degradation. Inaddition, the residual photoinitiator can be extracted or leach out ofthe cured article or migrate to the surface of the article, which isundesirable in many applications.

Increasingly stringent environmental protection legislation has promptedthe exploration and use of formulations which contain little or novolatile organic compounds (typically solvents). Thus the use offormulations with close to 100% reactive component is of great interest.

SUMMARY OF THE INVENTION

The present invention is directed to processes for radiation curing ofphotopolymerizable compounds using maleimides capable of initiatingphotopolymerization of radiation curable compounds, in place ofconventional photoinitiators. In contrast to conventionalphotoinitiators, substantially all of the maleimide is consumed duringinitiation and photopolymerization. Thus, the processes of the inventioncan eliminate the problems associated with residual photoinitiator inthe cured product, which are often observed when using conventionalphotoinitiators. The use of maleimides in accordance with the inventioncan also minimize the need for solvent based systems.

The maleimides can be useful as photoinitiators in thephotopolymerization of ethylenically unsaturated compounds, and inparticular, acrylate derivatives. The maleimides can also be useful ascomonomers with polymerizable compounds.

Maleimides useful in the processes of the invention include at least onemaleimide unit substituted at the nitrogen atom with a functionalizedaliphatic radical. Exemplary maleimide compounds include maleimides ofthe formula (I) below:

wherein:

(a) each R₁ and R₂ is independently selected from the group consistingof hydrogen, linear or branched C1 to C4 alkyl, and halogen;

(b) R is linear or branched C1 to C10 alkyl, heteroatom; or silicon; and

(c1) when R is C1 to C10 alkyl, FG is a functional group selected fromthe group consisting of —OR₃, —SR₃, —SiR₃, —OC(O)N(R₃)₂,—OC(O)C(═CHR₃)R₃, —OC(O)R₃, —C(O)R₃, —N(R₃)₂, —C(O)OR₃, —NCO,—C(O)N(R₃)₂, —OC(O)OR₃, —CN, halogen, —CH₂N-aryl-FG, —CH₂N-aryl-R₃—FG,sulfonic acid, quaternary ammonium, and salts thereof, with the provisothat when FG is —OR₃, R is C1 to C4 linear or branched alkyl, andfurther in which each R₃ is selected from the group consisting ofhydrogen, alkyl, aryl, cycloalkyl, arylalkyl, and alkylaryl, or

(c2) when R is a heterotom or silicon, FG is selected from the groupconsisting of hydrogen, alkyl, aryl, cycloalkyl, alkylaryl, arylalkyl,alkyl-FG′, and aryl-FG′, wherein FG′ is the same as FG as defined in(c1) above, or

FG is a functional group as defined in (c1) in combination with a spacergroup linking said maleimide unit with at least one other maleimide unitto form a di- or multifunctional maleimide compound.

The present invention also provides novel maleimides andphotopolymerizable compositions which include maleimide compoundscomprising at least one maleimide unit of Formula (I) above as acomponent thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

Some of the features and advantages of the invention having beendescribed, others will become apparent from the detailed descriptionwhich follows, and from the accompanying drawings, in which:

FIGS. 1-4 are graphs illustrating photopolymerization of HDDA withvarying levels of aliphatic maleimides;

FIGS. 5-9 are graphs illustrating photopolymerization of PEG400DA withvarying levels of aliphatic maleimides; and

FIG. 10 is a graph illustrating the consumption of an aliphaticmaleimide upon subsequent exposure to UV radiation.

DETAILED DESCRIPTION OF THE INVENTION

Aliphatic maleimide compounds useful in the invention include compoundshaving at least one maleimide unit substituted with a functionalizedaliphatic radical at the nitrogen atom. The aliphatic radical preferablyis a linear or branched C1 to C10 alkyl, and more preferably methyl orethyl. The alkyl is optionally substituted with C1 to C4 alkyl, C1 to C4alkoxy, halogen, and the like as described below.

The maleimide compound can be monofunctional (have one maleimidefunctional group), or can be di- or multi-functional (have two or moremaleimide functional groups). For example, two or more aliphaticmaleimide units can be connected or coupled via a spacer group(s), suchas, but not limited to, linear or branched C1 to C10 alkyl, C3 to C6cycloalkyl optionally substituted with C1 to C4 alkyl, C1 to C10oxyalkyl, which can include one or more oxygen atoms, such as thatderived from ethylene glycol, carbonate, and the like. Still further,maleimide compounds useful in the invention include maleimide unitsconnected to polymeric or oligomeric compounds (typically having amolecular weight of at least about 1000)

Exemplary maleimide compounds can have the formula (I) below:

wherein:

(a) each R₁ and R₂ is independently selected from the group consistingof hydrogen, linear or branched C1 to C4 alkyl, and halogen;

(b) R is linear or branched C1 to C10 alkyl, heteroatom; or silicon; and

(c1) when R is C1 to C10 alkyl, FG is a functional group selected fromthe group consisting of —OR₃, —SR₃, —SiR₃, —OC(O)N(R₃)₂,—OC(O)C(═CHR₃)R₃, —OC(O)R₃, —C(O)R₃, —N(R₃)₂, —C(O)OR₃, —NCO,—C(O)N(R₃)₂ , —OC(O)OR₃, —CN, halogen, —CH₂N-aryl-FG, —CH₂N-aryl-R₃—FG,sulfonic acid, quaternary ammonium, and salts thereof, in which each R₃is selected from the group consisting of hydrogen, alkyl, aryl,cycloalkyl, arylalkyl, and alkylaryl, or

(c2) when R is a heteratom or silicon, FG is selected from the groupconsisting of hydrogen, alkyl, aryl, cycloalkyl, alkylaryl, arylalkyl,alkyl-FG′, and aryl-FG′, wherein FG′is the same as FG as defined in (c1)above, or

FG is a functional group as defined in (c1) in combination with a spacergroup linking said maleimide unit with at least one other maleimide unitto form a di- or multifunctional maleimide compound. Exemplary spacergroups include without limitation linear or branched C1 to C10 alkyl, C3to C6 cycloalkyl, optionally substituted with lower C1 to C4 alkyl, C1to C10 oxyalkyl, which can include one or more oxygen atoms, such asthat derived from ethylene glycol, carbonate, and the like.

As used herein, the term alkyl refers to linear or branched C1 to C10alkyl, such as but not limited to methyl, ethyl, propyl, butyl,isopropyl, and the like, optionally substituted with halogen, aryl,arylalkyl, alkylaryl, cycloalkyl, alkoxy, heteroatoms, silicon, and thelike. The term cycloalkyl refers to C3 to C6 cycloalkyl, such as but notlimited to cyclopentyl and cyclohexyl, also optionally substituted withhalogen, aryl, alkyl, arylalkyl, alkylaryl, alkoxy, heteroatoms, siliconand the like. The term aryl refers to C3 to C10 cyclic aromatic groupssuch as but not limited to phenyl, naphthyl, and the like, optionallysubstitututed with halogen, alkyl, arylalkyl, alkylaryl, cycloalkyl,alkoxy, heteratoms, silicon, and the like. The term heteroatom refers tooxygen, sulfur, and nitrogen.

Exemplary maleimides useful in the process of the invention include, butare not limited to, hydroxy methylmaleimide (HMMI)(Ia)

hydroxy ethylmaleimide (HEMI) (Ib)

triethylene glycol biscarbonate bisethylmaleimide (Ib);

2ethylcarbonate ethylmaleimide (2ECEMI) (Id)

2-isopropyl urethane ethylmaleimide (2IPUEMI) (Ie)

2-acryloyl ethylmaleimide (2AEMI) (If)

acetoxy ethyl maleimide (AcOEMI) (Ig)

isophorone bisurethane bisethylmaleimide (IPBUBEMI) (Ih)

bisethylmaleimide carbonate (BEMIC) (Ii)

4,9-Dioxa-1,12 Dodecane Bismaleimide (4,9-DO-1,12-DDBMI) (Ij)

and the like.

Generally, maleimides compounds which include at least one maleimideunit of Formula (I) can be prepared using techniques known in the art.See, for example, Z. Y. Wang, Synthetic Comm. 20(11) 1607-1610 (1990);P. O. Tawney et al., J. Org. Chem. 26, 15 (1961); and U.S. Pat. No.2,542,145.

The present invention also provides photopolymerizable compositionswhich include an aliphatic maleimide as a component thereof, forexample, as a photoinitiator, a comonomer, and the like. As used herein,and as will be appreciated by the skilled artisan, the termphotopolymerizable composition refers to compositions which harden orcure upon exposure to radiation.

Generally the compositions of the invention include ethylenicallyunsaturated compounds, including monomers and oligomers derived fromacrylic and methacrylic acid, optionally dispersed or dissolved in asuitable solvent that is copolymerizable therewith, and mixturesthereof, which are photopolymerizable when exposed to a source ofradiation (ultraviolet or UV radiation, or radiation outside the UVspectrum), particularly free radical polymerizable systems. As will beappreciated by the skilled artisan, the photopolymerizable compounds canbe monofunctional, or can include two or more polymerizableethylenically unsaturated groupings per molecule.

Exemplary photopolymerizable compounds or precursors include, but arenot limited to, reactive vinyl monomers, including acrylic monomers,such as acrylic and methacrylic acids, and their amides, esters, saltsand corresponding nitriles. Suitable vinyl monomers include, but are notlimited to, methyl acrylate, ethyl acrylate, n- or tert-butylacrylate,isooctyl acrylate, methyl methacrylate, ethylmethacrylate, 2-ethylhexylmethacrylate, butylacrylate, isobutyl methacrylate, the correspondinghydroxy acrylates, i.e., hydroxy ethylacrylate, hydroxy propylacrylate,hydroxy ethylhexyl methacrylate, glycol acrylates, i.e., ethylene glycoldimethacrylate, hexamethylene glycol dimethacrylate, the allylacrylates, i.e., allyl methacrylate, diallyl methacrylate, the epoxyacrylates, i.e., glycidyl methacrylate, and the aminoplast acrylates,i.e., melamine acrylate. Others such as vinyl acetate, vinyl andvinylidene halides and amides, i.e., methacrylamide, acrylamide,diacetone acrylamide, vinyl and vinylidene esters, vinyl and vinylideneethers, vinyl and vinylidene ketones, butadiene, vinyl aromatics, i.e.,styrene, alkyl styrenes, halostyrenes, alkoxystyrenes, divinyl benzenes,vinyl toluene, and the like are also included. Prepolymers includeacrylated epoxides, polyesters and polyurethanes, and are typicallycombined with a suitable monomer for viscosity control.

The photopolymerizable compounds may be polymerized to form homopolymersor copolymerized with various other monomers.

The photopolymerizable compound can be present in the compositions ofthe invention in amounts from about 99.99 to about zero percent byweight based on the total weight of the composition.

The maleimides compounds which include at least one maleimide unit ofFormula (I) can be used singly or as a mixture thereof, and are usefulas photopolymerization initiators. In this aspect of the invention, themaleimide compounds can be present in the photopolymerizable compositionin an amount sufficient to initiate polymerization thereof upon exposureto radiation. The composition can include about 0.01 to about 100percent by weight maleimide compound, based on the total weight of thephotopolymerizable compounds. The maleimides are particularlyadvantageous for use in “photoinitiator-free” systems, in which themaleimide(s) replace conventional photoinitiators. Although not wishingto be bound by any explanation of the invention, it is believed that thealiphatic maleimides can initiate polymerization via hydrogenabstraction mechanisms.

The photopolymerizable compositions of the invention may also containother conventional agents, such as polymerization inhibitors, fillers,ultraviolet absorbers and organic peroxides. It can also be advantageousto also include as a component of the compositions of the invention acoinitiator or synergist, that is, a molecule which serves as a hydrogenatom donor or an electron donor. Coinitiators or synergists are known inthe art, and are typically alcohols, tertiary amines or ethers whichhave available hydrogens attached to a carbon adjacent to a heteroatom.Such coinitiators are typically present in an amount between about 0.2and about 25 percent by weight based on the total weight of thecomposition. Suitable compounds include, but are not limited to,triethanolamine, methyl-diethanolamine, ethyldiethanolamine and estersof dimethylamino benzoic acid. Other known coinitiators or acceleratorscan also be used. These compounds behave as coinitiators or acceleratorsfor the primary photoinitiators and can increase the efficiency andspeed of the polymerization process.

The photopolymerizable compositions can be applied or deposited on asurface of a substrate using conventional techniques and apparatus. Thecomposition can be applied as a substantially continuous film.Alternatively, the composition can be applied in a discontinuouspattern. The thickness of the deposited composition can vary, dependingupon the desired thickness of the resultant cured product. One advantageof the invention is that relatively thick coatings of polymerizablecompositions. For example, the inventors have found that PEG400DAcomprising 2 to 10% by mole ECMI or 2AEMI can be effective for a 1.5 to7 cm thick or bulk composition using a medium pressure mercury lamp (30mW/cm).

Typically, the substrate is coated with the uncured photopolymerizablecomposition and passed under a commercially available UV or excimer lampon a conveyer moving at predetermined speeds. The substrate to be coatedcan be, for example, metal, wood, mineral, glass, paper, plastic,fabric, ceramic, and the like.

The active energy beams used in accordance with the present inventionmay be visible light or ultraviolet light or may contain in theirspectra both visible and ultraviolet light. The polymerization may beactivated by irradiating the composition with ultraviolet light usingany of the techniques known in the art for providing ultravioletradiation, i.e., in the range of 200 nm and 450 nm ultravioletradiation, and especially with the 308 nm emission from xenon chlorideexciter lamps, commercially available from Fusion Systems, or byirradiating the composition with radiation outside of the ultravioletspectrum. The radiation may be natural or artificial, monochromatic orpolychromatic, incoherent or coherent and should be sufficiently intenseto activate the photoinitiators of the invention and thus thepolymerization. Conventional radiation sources include fluorescentlamps, excimer lamps, mercury, metal additive and arc lamps. Coherentlight sources are the pulsed nitrogen, xenon, argon ion- and ionizedneon lasers whose emissions fall within or overlap the ultraviolet orvisible absorption bands of the compounds of the invention.

The compositions are useful in any of the types of applications known inthe art for photopolymerizations, including as a binder for solids toyield a cured product in the nature of a paint, varnish, enamel,lacquer, stain or ink. The compositions can also be useful in theproduction of photopolymerizable surface coatings in printing processes,such as lithographic printing, screen printing, and the like. Thecompositions can also be useful in applications in which thecompositions are applied to articles which are to be exposed to theenvironment, such as signage. Radiation cured coatings produced usingconventional photoinitators typically degrade over time (as evidenced byyellowing, increasing brittleness, and the like), which degradation isexacerbated by direct exposure to sunlight. In contrast, radiation curedcoatings prepared using the maleimide compounds can exhibit minimaldegradation over time, even when exposed to direct sunlight. Themaleimides can also be water soluble.

The present invention will be further illustrated by the followingnon-limiting examples.

EXAMPLE 1 Synthesis of Hydroxy Methylmaleimide (HMMI)

Maleimide (10 g, 0.103 mol) was added to 10 mL of a 37% solution offormaldehyde and 0.31 mL of a 5% solution of NaOH was added. Within 10minutes all of the maleimide had dissolved and an exothermic reactionproceeded. The solution was stirred for 2 hours where white crystalswere observed. The solution was placed in a freezer overnight and theresulting crystals filtered and washed with ice cold ethanol and diethylether. The white crystals were purified twice by sublimation. See P. O.Tawney, R. H. Snyder, R. P. Conger, K. A. Leibbrand, C. H. Stiteler, andA. R. Williams J. Org. Chem. 26, 15 (1961).m.p. 104-106° C. (9.77 g,74.6%). ¹H-NMR (Acetone-d₆, δ, ppm): 4.96 (2H, —CH₂—, s), 5.33 (1H, —OH,s), 6.93 (2H, —CH═CH—, s). ¹³C—NMR (Acetone-d₆, δ, ppm): 60.9 (1C,—CH₂—), 135.6 (2C, —CH═CH—), 173.1 (1C, —C═O).

EXAMPLE 2 Synthesis of Hydroxy Ethylmaleimide (HEMI)

Ethanolamine (80.96 g, 1.32 mol) was added to 500 mL of ethanol andcooled to 0° C. using an ice bath. 3,6-Endoxo-1,2,3,6-tetrahydrophthalicanhydride (220.21 g, 1.32 mol) was added to the solution and allowed tostir overnight. The yellow tinted crystals were used withoutpurification. The solution was refluxed for four hours with azeotropicremoval of water. The solution was cooled to 0° C. and the resultingcrystals filtered (151.74 g, 54.95%). Removal of furan was facilitatedby refluxing the crystals in xylenes for 4 hours with quantitative yieldof hydroxy ethylmaleimide after purification by sublimation to yieldwhite crystals, —CH₂O—), 134.2 (2C, —CH═CH—), 171.2 (2C, —NC═O m.p. 68°C. ¹H-NMR (CDCl₃, δ, ppm): 2.62 (1H, —OH, s), 3.82-3.77 (4H, —NCH₂CH₂O—,overlapping), 6.76 (2H, —CH═CH—, s). ¹³C-NMR (CDCl₃, δ, ppm): 40.5 (1C,—NCH₂—), 60.5 (1C,).

EXAMPLE 3 Triethylene Glycol Biscarbonate Bisethylmaleimide (TEGBCBEMI)

HEMI (25.65 g, 0.182 moles) and pyridine (14.38 g, 0.182 moles) weredissolved in THF (130 mL) and the solution was stirred at roomtemperature. Triethylene glycol bischloroformate (25.0 g, 0.091 moles)was added dropwise and stirred for 90 minutes. The pyridine salt wasfiltered off and the solution was combined with 200 mL of a 1N HClsolution. The product was extracted with methylene chloride and washedwith a 1N HCl solution followed by water and then dried over magnesiumsulfate. The red solution was diluted to a volume of 150 mL and purifiedby column chromatography (2.5 cm×21 cm) using silica gel as the packingand methylene chloride as the mobile phase yielding white crystals, m.p.65° C. (26.75 g, 60.76%). ¹H-NMR (CDCl₃), δ, ppm): 3.64-3.68 (4Hφ—OCH₂—, t), 3.69-3.74 (4H, ε—OCH₂—, t), 3.81-3.86 (4H, —NCH₂—, t),4.26-4.3 (8H, —CH₂O(C═O)OCH₂—, t), 6.75 (4H, —CH═CH—, s). ¹³C-NMR(CDCl₃, δ, ppm): 36.6 (2C, —NCH₂—), 64.7 (2C, ), 67.3 (2C, ), 68.8 (2C,), 70.6 (2C, ), 134.4 (4C, —CH═CH—), 154.8 (2C, O(C═O)O), 170.4 (4C,—NC═O).

EXAMPLE 4 Synthesis of 2-Ethylcarbonate Ethylmaleimide (2ECEMI)

Hydroxy ethylmaleimide (29.87 g, 0.212 moles) and pyridine (16.7 g,0.212 moles) were dissolved in THF (170 mL) and the solution was stirredat room temperature. Ethyl chloroformate (22.97 g, 0.212 moles) wasadded dropwise and stirred for 90 minutes. The pyridine salt wasfiltered off and the solution was combined with 200 mL of a 1N HClsolution. The product was extracted with methylene chloride and washedwith a 1N HCl solution followed by water and then dried over magnesiumsulfate. The red solution was concentrated and the red crystals purifiedby sublimation yielding white crystals, m.p. 52° C. (34.76 g, 77.04% ).¹H-NMR (CDCl₃), δ, ppm): 1.26-1.34 (3H, —CH₃, t), 3.81-3.87 (2H —NCH₂—,t), 4.14-4.25 (2H, δ-CH₂OC═O, q), 4.25-4.30 (2H, β-CH₂O—, t), 6.74 (2H,—CH═CH—, s). ¹³C—NMR (CDCl₃, δ, ppm): 14.2 (1C, —CH₃), 36.8 (1C,—NCH₂—), 64.3 (1C, δ—CH₂O), 64.5 (1C, δ—CH₂—), 134.4 (2C, —CH═CH—),154.9 (1C, O(C═O)O), 170.4 (2C, —C═O).

EXAMPLE 5 Synthesis of 2-Isopropyl Urethane Ethylmaleimide (2IPUEMI)

Hydroxy ethylmaleimide (5 g, 35.4 mmol) was dissolved in 75 mL ofmethylene chloride 1 drop of dibutyl tin dilaurate catalyst was added.Isopropyl isocyanate (3.01 g, 35.4 mmol) was added dropwise and thesolution was stirred for 3 hours. The solution was washed with waterdried with magnesium sulfate. Concentration yielded white crystals whichwere further purified sublimation yielding white crystals, m.p. 117° C.(6.49 g, 81%). ¹H-NMR (CDCl₃, δ, ppm): 1.11-1.14 (6H, —C(CH₃)₂, d),3.74-3.79 (2H, —NCH₂—, t), 4.28-4.32 (2H, —CH₂O—, t), 4.44-4.53 (1H,—CH—, p), 6.72 (2H, —OC—CH═CH—CO—, s). NMR ¹³C—NMR (CDCl₃, δ, ppm):170.5 (2C, C═O, maleimide), 155.1 (1C, C═O, urethane), 134.2 (2C,—CH═CH—), 61.7 (1C, β—CH₂), 43.6 (1C, —CH—), 37.4 (1C, α—CH₂), 22.9 (2C,—CH₃).

EXAMPLE 6 Synthesis of 2-Acryloyl Ethylmaleimide (2AEMI)

2-Hydroxyethyl maleimide (5 g, 35.4 mmol) and Et₃N (4.25 g, 43.0 mmol)was dissolved in 75 mL of methylene chloride and cooled to 0° C.Acryloyl chloride (3.20 g, 35.4 mmol) in 25 mL of methylene chloride wasadded dropwise over 30 minutes. The solution was stirred at roomtemperature for 30 minutes followed by refluxing for 1 hour. Thetriethylamine hydrochloride was removed by filtration and the yellowsolution was concentrated. The yellow crystals were purified bysublimation yielding white crystals, m.p. 77-78° C. (5.00 g, 72.3%).¹H-NMR (CDCl₃, δ, ppm): 3.81-3.87 (2H, —NCH₂—, t) 4.22-4.33 (2H, —OCH₂—,t), 5.81-5.85 (2H, CH₂═CH, cis), 6.00-6.13 (1H, CH₂═CH—,q), 6.34-6.42(1H CH₂═CH, trans), 6.73 (2H, —OC—CH═CH—CO—, s). ¹³C—NMR (CDCl₃, δ,ppm): 170.4 (2C, C═O, maleimide), 165.8 (1C, C═O, ester), 134.2 (2C,—CH═CH—), 131.45 (1C, —CH═), 127.9 (1C, CH₂═), 61.5 (1C, β-CH₂—), 36.8(1C, α-CH₂—).

EXAMPLE 7 Synthesis of Acetoxy Ethyl Maleimide (AcOEMI)

Maleic anhydride (172.32 g, 1.75 mol) was added to ethanolamine (107.34g, 1.75 mol) and dissolved in 500 mL of acetone while stirring overnightin an ice bath. To the solution, 400 mL of acetic anhydride (4.23 mol)was added with sodium acetate (144 g, 1.75 mol). The solution was heatedto 80° C. and stirred for 1 hour. The contents were poured into icewater and the acetic acid neutralized with K₂CO₃. The product wasextracted with methylene chloride and then dried using magnesiumsulfate. The product was purified by sublimation yielding whitecrystals, m.p. 76° C. (44.1 g, 13.45%) ¹H-NMR (CDCl₃, δ, ppm): 2.02 (3H,—CH₃, s), 3.82-3.77 (2H, —NCH₂—, t), 4.25-4.20 (2H, —CH₂O—, t), 6.75(2H, —CH═CH—, s). ¹³C—NMR (CDCl₃, δ, ppm): 20.7 (1C, —CH3), 37.0 (1C,—NCH₂—), 61.5 (1C, —CH₂O—), 134.3 (2C, —CH═CH—), 170.5 (2C, —NC═O),170.8 (1C, —OC═O).

EXAMPLE 8 Synthesis of 4,9-Dioxa-1,12 Dodecane Bismaleimide(4,9-DO-1,12-DDBMI)

4,9-Dioxa-1,12-dodecane diamine (25 g, 0.122 mol) was dissolved inacetone and added dropwise to a solution of maleic anhydride (24 g 0.244mol) in 120 mL of acetone under cooling using an ice bath in a nitrogenatmosphere. The solution was stirred overnight and the contents werethen poured into water and the bismaleamic acid filtered and washed withethanol and diethylether.

The bismaleamic acid (29.96 g, 74.8 mmol) was dissolved in an acetone120 mL and triethylamine (41.7 mL, 0.300 mol) solution. The solution washeated to reflux, where acetic anhydride (21.2 mL, 0.224 mol) was addeddropwise, the solution was refluxed for 12 hours. The solution was addedto ice water and the precipitate filtered and dried. The sample waspurified by column chromatography using silica gel as the adsorbent andmethylene chloride as the mobile phase yielding white crystals, m.p. 65°C. (5.5 g, 20.2%). ¹H-NMR (CDCl₃, δ, ppm): 1.60-1.54 (2H, ε—CH₂—),1.91-1.78 (2H, β—CH₂—), 3.44-3.28 (4H, —CH₂OCH₂—), 3.66-3.59 (2H,—NCH₂—, t), 6.70 (2H, —CH═CH—, s). ¹³C-NMR (CDCl₃, δ, ppm): 26.4 (2C,ε—CH₂—), 28.6 (2C, β-CH₂—), 35.6 (2C, —NCH₂—), 68.2, 70.7 (4C,—CH₂OCH₂—), 134.2 (2C, —CH═CH—), 170.8 (2C, —NC═O).

EXAMPLE 9 Synthesis of Isophorone Bisurethane Bisethylmaleimide(IPBUBEMI)

Hydroxy ethylmaleimide (10 g, 0.141 mol) was dissolved in acetone andpurged with nitrogen while stirring in an ice bath. One drop of dibutyltin dilaurate was added to the solution. The isophorone diisocyanate(30.5 g, 0.141 mol) was added dropwise over 2-3 hours. The solution wasallowed to stir overnight and a white precipitate was obtained aftersolvent removal m.p. 105-112° C. (40.5 g, 100%). ¹H-NMR (D₆—DMSO, δ,ppm): 3.63-3.58 (2H, —NCH₂—), 4.08-4.03 (2H, —CH₂O—, t), 7.03 (2H,—CH═CH—, s). ¹³C-NMR (D₆—DMSO, δ, ppm): 134.5 (2C, —CH═CH—), 154.9 (2C,NHC═O), (170.7 (2C, —NC═O).

EXAMPLE 10 Synthesis of Bispropyl Maleimide (PBMI)

Diaminopropane was dissolved in 100 mL of dimethyl acetamide (DMAC) andadded dropwise to a solution of maleic anhydride in DMAC under coolingusing an ice bath in a nitrogen atmosphere. The solution was stirredovernight and the contents were then poured into water and thebismaleamic acid filtered and washed with ethanol and diethylether.

The bismaleamic acid (84.54 g, 0.312 mol) was dissolved in 312 mL of anacetone and triethylamine (87 mL, 0.624 mol) solution. The solution washeated to reflux and acetic anhydride (88 mL, 0.61 mol) was addeddropwise through a reflux condenser and the solution was refluxed for 12hours. The solution was added to ice water and the precipitate filteredand dried. The sample was purified by column chromatography using silicagel as the adsorbent and methylene chloride as the mobile phase yieldingwhite crystals, m.p. 166° C. (19.28 g, 26.3%). ¹H-NMR (CDCl₃, δ, ppm):2.00-1.86 (2H, —CH₂—, p), 3.57-3.50 (4H, —NCH₂—, t), 6.71 (2H, —CH═CH—,s). ¹³C-NMR (CDCl₃, δ, ppm): 27.3 (1C, —CH₂—), 35.3 (2C, —NCH₂—), 134.2(2C, —CH═CH—), 170.6 (2C, —NC═O).

EXAMPLE 11 Synthesis of Bisethylmaleimide Carbonate (BEMIC)

Hydroxy ethylmaleimide (10.0 g, 70.1 mmol) was dissolved in a solutionof methylene chloride (71 mL) and triethylamine (9.87 mL, 70.8 mmol) andcooled with an ice bath to 0° C. Triphosgene (3.504 g, 12 mmol) wasadded over a period of 4 hours and the resulting solution filtered. Thesupernatant was washed with 1N hydrochloric acid, 5% potassium carbonatesolution and water. The solution was dried over magnesium sulfate andpurified using activated carbon to yield white crystals (4.0 g, 18.5%).¹H-NMR (CDCl₃, δ, ppm): 3.82 (4H, —NCH₂—, t), 4.27 (2H, —CH₂O—, t), 6.73(2H, —CH═CH—, s). ¹³C-NMR (CDCl₃, δ, ppm): 36.6 (2C, —NCH₂—), 64.9 (2C,—CH₂O—), 134.2 (2C, —CH═CH—), 154.5 (1C, C═O) 170.8 (2C, —NC═O).

EXAMPLE 12 Photopolymerization

Photo-DSC results (FIGS. 1-8) established that the compounds of theinvention photoinitiate polymerization of hexanediol diacrylate (HDDA)and polyethylene glycol diacrylate (PEG400DA). Additional monomers andcrosslinked polymers may also be photoinitiated by these compounds. Thephoto-DCS traces show the relative performance of the compounds of theinvention in the peak heat release rate, and in the time required toreach the peak rate.

A comparative example of photopolymerization of PEG400DA with dimethoxyphenylacetophenone (DMPA) and ECEMI (FIG. 9) shows that both compoundsphotoinitiate.

UV absorbance of a formulation of 10 mole percent ECEMI in PEG400DA wasmeasured before and after curing a 25 micron film under a Fusion H bulbat a belt speed of 80 feet per minute (FIG. 10). The characteristicabsorbance of the maleimide is reduced after one pass under the lamp andis reduced further after five passes under the lamp. This establishesthat the maleimide is indeed consumed and no measurable photo-byproductsare created.

The foregoing examples are illustrative of the present invention and arenot to be construed as limiting thereof.

That which is claimed is:
 1. An aliphatic maleimide of the formula:

wherein: (a) each R₁ and R₂ is independently selected from the groupconsisting of hydrogen, linear or branched C1 to C4 alkyl, and halogen;(b) R is linear or branched C1 to C10 alkylene; and (c) FG is afunctional group selected from the group consisting of —OR₃, —SR₃,—SiH₂R₃, —OC(O)N(R₃)₂, —C(O)R₃, —C(O)OR₃, —NCO, —C(O)N(R₃)₂, —OC(O)OR₃,—OC(O)R₃, —CH₂N-aryl-FG′, —CH₂N-aryl-R₃′,—FG′, sulfonic acid, quaternaryammonium, and salts thereof, in which each R₃ is selected from the groupconsisting of hydrogen, alkyl, aryl, cycloalkyl, arylalkyl, andalkylaryl, and R₃′, is selected from the group consisting of alkylene,arylene, cycloalkylene, arylalkylene, and alkylarylene, with the provisothat when FG is —OR₃, then R₃ is not hydrogen, or when FG is—OC(O)N(R₃)₂, then R₃ is not aryl, or when FG is —OC(O)R₃, then R₃ isnot alkyl, or when FG is —C(O)OR₃, then R₃ is not hydrogen, and in whichFG′is selected from the group consisting of —OR₃, —SR₃, —SiH₂R₃,—OC(O)N(R₃)₂, —OC(O)C(═CHR₃)R₃, —OC(O)R₃, —C(O)R₃, —N(R₃)₂, —C(O)OR₃,—NCO, —C(O)N(R₃)₂, —OC(O)OR₃, —CN, halogen, sulfonic acid, andquaternary ammonium.
 2. The maleimide of claim 1, wherein FG is afunctional group selected from the group consisting of —SR₃, —SiH₂R₃,—NCO, —CN, —CH₂N-aryl-FG′, —CH₂N-aryl-R₃′, —FG′, sulfonic acid, andsalts thereof, in which each R₃ is selected from the group consisting ofalkyl, aryl, cycloalkyl, arylalkyl, and alkylaryl and R₃′ is selectedfrom the group consisting of alkylene, arylene, cycloalkylene,arylalkylene, and alkylarylene and in which FG′ is selected from thegroup consisting of —OR₃, —SR₃, —SiH₂R₃, —OC(O)N(R₃)₂, —OC(O)C(═CHR₃)R₃,—OC(O)R₃, —C(O)R₃, —N(R₃)₂, —C(O)OR₃, —NCO, —C(O)N(R₃)₂, —OC(O)OR₃, CN,halogen, sulfonic acid, and quaternary ammonium.
 3. An aliphaticmaleimide, wherein said maleimide is 2-ethylcarbonate ethylmaleimide(2ECEMI)


4. An aliphatic maleimide, wherein said maleimide is 2-isopropylurethane ethylmaleimide (2IPUEMI)


5. An aliphatic maleimide of the formula:

wherein: (a) each R₁ and R₂ is independently selected from the groupconsisting of hydrogen, linear or branched C1 to C4 alkyl, and halogen;(b) R is oxygen, sulfur, nitrogen or —SiH₂—; and (c) FG is selected fromthe group consisting of hydrogen, alkyl, aryl, cycloalkyl, alkylaryl,arylalkyl, alkyl-FG″, and aryl-FG″, wherein FG″is a functional groupselected from the group consisting of —OR₃, —SR₃, —SiH₂R₃, —OC(O)N(R₃)₂,—OC(O)C(═CHR₃)R₃, —OC(O)R₃, —C(O)R₃, —N(R₃)₂, —C(O)OR₃, —NCO,—C(O)N(R₃)₂, —OC(O)OR₃, —CN, halogen, sulfonic acid, quaternaryammonium, and salts thereof, and in which each R₃ is selected from thegroup consisting of hydrogen, alkyl, aryl, cycloalkyl, arylalkyl, andalkylaryl.
 6. A multi-functional aliphatic maleimide of the formula:

wherein: (a) each R₁ and R₂ is independently selected from the groupconsisting of hydrogen, linear or branched C1 to C4 alkyl, and halogen;(b) R is linear or branched C1 to C10 alkylene, oxygen, sulfur,nitrogen, or —SiH₂—; and (c) FG comprises a functional group derivedfrom the group consisting of —OR₃, —SR₃, —SiH₂R₃, —OC(O)N(R₃)₂,—OC(O)C(═CHR₃)R₃, —OC(O)R₃, —C(O)R₃, —N(R₃)₂, —C(O)OR₃, —NCO,—C(O)N(R₃)₂, —OC(O)OR₃, —CN, halogen, —CH₂N-aryl-FG′, —CH₂N-aryl-R₃—FG′,sulfonic acid, quaternary ammonium, and salts thereof, in which each R₃is selected from the group consisting of hydrogen, alkyl, aryl,cycloalkyl, arylalkyl, and alkylaryl and in which FG′ is selected fromthe group consisting of —OR₃, —SR₃, —SiH₂R₃, —OC(O)N(R₃)₂,—OC(O)C(═CHR₃)R₃, —OC(O)R₃, —C(O)R₃, —N(R₃)₂, —C(O)OR₃, —NCO,—C(O)N(R₃)₂, —OC(O)OR₃, —CN, halogen, sulfonic acid, and quaternaryammonium in combination with a spacer group selected from the groupconsisting of linear or branched C1-C10 alkylene, C3-C6 cycloalkyleneoptionally substituted with C1-C4 alkyl, and C1-C10 oxyalkylene linkingsaid maleimide unit with at least one other maleimide unit to form amulti-functional maleimide compound, with the proviso that when saidspacer group comprises an oxyalkylene and FG comprises a carbonategroup, then R is not alkylene.
 7. The maleimide of claim 6, wherein R islinear or branched C1 to C10 alkylene.
 8. The maleimide of claim 6,wherein R is oxygen, sulfur, nitrogen, or —SiH₂—.
 9. The maleimide ofclaim 6, wherein FG comprises a carbonate functional group.
 10. Themaleimide of claim 6, wherein FG comprises a urethane functional group.11. The maleimide of claim 6, wherein said spacer group comprises atleast one polyethylene glycol group.
 12. An aliphatic maleimide, whereinsaid maleimide is triethylene glycol biscarbonate bisethylmaleimide(TEGBCBEMI)


13. An aliphatic maleimide, wherein said maleimide is isophoronebisurethane bisethylmaleimide (IPBUBEMI)


14. A di-functional aliphatic maleimide of the formula:

wherein: (a) each R₁ and R₂ is independently selected from the groupconsisting of hydrogen, linear or branched C1 to C4 alkyl, and halogen;(b) R is linear or branched C1 to C10 alkylene, oxygen, sulfur,nitrogen, or —SiH₂—; and (c) FG comprises a functional group derivedfrom the group consisting of —OR₃, —SR₃, —SiH₂R₃, —OC(O)N(R₃)₂,—OC(O)C(═CHR₃)R₃, —OC(O)R₃, —C(O)R₃, —N(R₃)₂, —C(O)OR₃, —NCO,—C(O)N(R₃)₂, —OC(O)OR₃, —CN, halogen, —CH₂N-aryl-FG′, —CH₂N-aryl-R₃—FG′,sulfonic acid, quaternary ammonium, and salts thereof, in which each R₃is selected from the group consisting of hydrogen, alkyl, aryl,cycloalkyl, arylalkyl, and alkylaryl and in which FG′ is selected fromthe group consisting of —OR₃, —SR₃, —SiH₂R₃, —OC(O)N(R₃)₂,—OC(O)C(═CHR₃)R₃, —OC(O)R₃, —C(O)R₃, —N(R₃)₂, —C(O)OR₃, —NCO,—C(O)N(R₃)₂, —OC(O)OR₃, —CN, halogen, sulfonic acid, and quaternaryammonium, wherein FG further comprises a spacer group selected from thegroup consisting of linear or branched C1-C10 alkylene, C3-C6cycloalkylene optionally substituted with C1-C4 alkyl, and C1-C10oxyalkylene linking said maleimide unit with at least one othermaleimide unit to form a di-functional maleimide compound, with theproviso that when said spacer group comprises an oxyalkylene and FGcomprises a carbonate group, then R is not alkylene.
 15. A di-functionalaliphatic maleimide of the formula:

wherein: (a) each R₁ and R₂ is independently selected from the groupconsisting of hydrogen, linear or branched C1 to C4 alkyl, and halogen;(b) R is linear or branched C1 to C10 alkylene, oxygen, sulfur,nitrogen, or —SiH₂—; (c) FG is derived from the reaction of a functionalgroup selected from the group consisting of —OR₃, —SR₃, —SiH₂R₃,—OC(O)N(R₃)₂, —OC(O)C(═CHR₃)R₃, —OC(O)R₃, —C(O)R₃, —N(R₃)₂, —C(O)OR₃,—NCO, —C(O)N(R₃)₂, —OC(O)OR₃, —CN, halogen, —CH₂N-aryl-FG′,—CH₂N-aryl-R₃—FG′, sulfonic acid, quaternary ammonium, and saltsthereof, in which each R₃ is selected from the group consisting ofhydrogen, alkyl, aryl, cycloalkyl, arylalkyl, and alkylaryl and in whichFG′ is selected from the group consisting of —OR₃, —SR₃, —SiH₂R₃,—OC(O)N(R₃)₂, —OC(O)C(═CHR₃)R₃, —OC(O)R₃, —C(O)R₃, —N(R₃)₂, —C(O)OR₃,—NCO, —C(O)N(R₃)₂, —OC(O)OR₃, —CN, halogen, sulfonic acid, andquaternary ammonium with a spacer group SP; and (d) SP is a spacer grouplinking said maleimide unit with at least one other maleimide unit toform a di-functional maleimide compound, said spacer group selected fromthe group consisting of linear alkylene, branched alkylene,cycloalkylene, and oxyalkylene groups, with the proviso that when SP isoxyalkylene and FG comprises a carbonate group, then R is not alkylene.16. A multi-functional aliphatic maleimide of the formula:

wherein: (a) each R₁ and R₂ is independently selected from the groupconsisting of hydrogen, linear or branched C1 to C4 alkyl, and halogen;(b) each R is linear or branched C1 to C10 alkyl, oxygen, sulfur,nitrogen, or —SiH₂—; (c) each FG is derived from the reaction of afunctional group selected from the group consisting of —OR₃, —SR₃,—SiH₂R₃, —OC(O)N(R₃)₂, —OC(O)C(═CHR₃)R₃, —OC(O)R₃, —C(O)R₃, —N(R₃)₂,—C(O)OR₃, —NCO, —C(O)N(R₃)₂, —OC(O)OR₃, —CN, halogen, —CH₂N-aryl-FG′,—CH₂N-aryl-R₃—FG′, sulfonic acid, quaternary ammonium, and saltsthereof, in which each R₃is selected from the group consisting ofhydrogen, alkyl, aryl, cycloalkyl, arylalkyl, and alkylaryl and in whichFG′is selected from the group consisting of —OR₃, —SR₃, —SiH₂R₃,—OC(O)N(R₃)₂, —OC(O)C(═CHR₃)R₃, —OC(O)R₃, —C(O)R₃, —N(R₃)₂, —C(O)OR₃,—NCO, —C(O)N(R₃)₂, —OC(O)OR₃, —OC(O)R₃, —CN, halogen, sulfonic acid, andquaternary ammonium with a spacer group SP; (d) SP comprises a spacergroup selected from the group consisting of linear or branched C1-C10alkylene, C3-C6 cycloalkylene optionally substituted with C1-C4 alkyl,and C1-C10 oxyalkylene linking said maleimide unit with at least oneother maleimide unit to form a multi-functional maleimide compound, withthe proviso that when said spacer group comprises an oxyalkylene and FGcomprises a carbonate group, then R is not alkylene; and (e) n isgreater than
 2. 17. A di-functional aliphatic maleimide of the formula:

wherein: (a) each R₁ and R₂ is independently selected from the groupconsisting of hydrogen, linear or branched C1 to C4 alkyl, and halogen;(b) R is linear or branched C2 to C10 alkylene, oxygen, sulfur,nitrogen, or —SiH₂; (c) FG is derived from the reaction of a functionalgroup selected from the group consisting of —OR₃, —SR₃, —SiH₂R₃,—OC(O)N(R₃)₂, —OC(O)C(═CHR₃)R₃, —OC(O)R₃, —C(O)R₃, —N(R₃)₂, —C(O)OR₃,—NCO, —C(O)N(R₃)₂, —OC(O)OR₃, —CN, halogen, —CH₂N-aryl-FG′,—CH₂N-aryl-R₃—FG′, sulfonic acid, quaternary ammonium, and saltsthereof, in which each R₃ is selected from the group consisting ofhydrogen, alkyl, aryl, cycloalkyl, arylalkyl, and alkylaryl and in whichFG′ is selected from the group consisting of —OR₃, —SR₃, —SiH₂R₃,—OC(O)N(R₃)₂, —OC(O)C(═CHR₃)R₃, —OC(O)R₃, —C(O)R₃, —N(R₃)₂, —C(O)OR₃,—NCO, —C(O)N(R₃)₂, —OC(O)OR₃, —CN, halogen, sulfonic acid, andquaternary ammonium with a spacer group SP; and (d) SP is a spacer grouplinking said maleimide unit with at least one other maleimide unit toform a di-functional maleimide compound, said spacer group comprising aC1 to C10 polyalkylene glycol, with the proviso that when FG comprises acarbonate functionality, then R is not alkylene.
 18. A di-functionalaliphatic maleimide of the formula:

wherein: (a) each R₁ and R₂ is independently selected from the groupconsisting of hydrogen, linear or branched C1 to C4 alkyl, and halogen;(b) R is linear or branched C1 to C10 alkylene, oxygen, sulfur,nitrogen, or —SiH₂; (c) FG is derived from the reaction of a functionalgroup selected from the group consisting of —OR₃, —SR₃, —SiH₂R₃,—OC(O)N(R₃)₂, —OC(O)C(═CHR₃)R₃, —OC(O)R₃, —OR₃O—, —N(R₃)₂, —C(O)OR₃,—NCO, —C(O)N(R₃)₂, —OC(O)OR₃, —CN, halogen, —CH₂N-aryl-FG′,—CH₂N-aryl-R₃—FG′, sulfonic acid, quaternary ammonium, and saltsthereof, in which each R₃ is selected from the group consisting ofhydrogen, alkyl, aryl, cycloalkyl, arylalkyl, and alkylaryl and in whichFG′ is selected from the group consisting of —OR₃, —SR₃, —SiH₂R₃,—OC(O)N(R₃)₂, —OC(O)C(═CHR₃)R₃, —OC(O)R₃, —C(O)R₃, —N(R₃)₂, —C(O)OR₃,—NCO, —C(O)N(R₃)₂, —OC(O)OR₃, —CN, halogen, sulfonic acid, andquaternary ammonium with the R group.